Selective hydrogenations of unsaturated hydrocarbon compounds are of high industrial significance. The pyrolysis of naphtha for the production of ethene, propene, butanes, 1,3-butadiene and aromatic compounds is a key process in the modern petrochemical industry. For the nearly complete removal of alkynic compounds from the C2, C3 and C4 cuts, selective hydrogenations are generally used.
For instance, the hydrogenation of acetylene is an important industrial process to remove traces of acetylene in the ethylene feed for the production of polyethylene. Because acetylene poisons the catalyst for the polymerisation of ethylene to polyethylene, the acetylene content in the ethylene feed has to be reduced to the low ppm range. Moreover, economic efficiency requires high selectivity of acetylene hydrogenation in the presence of an excess of ethylene to avoid the hydrogenation of a large fraction of the ethylene to ethane.
Palladium shows high activity for hydrogenation, in particular the hydrogenation of acetylene, but its selectivity is limited. In particular at high acetylene conversion, palladium will completely hydrogenate acetylene to ethane, convert ethylene to ethane, and form C4Hx and higher hydrocarbons by oligomerization reactions. In addition, deactivation of Pd during acetylene hydrogenation is caused by carbon and hydrocarbon deposits and necessitates frequent regeneration and/or exchange of the catalyst.
The C3 cut (propylene) is generally purified by selective hydrogenation of propyne (methylacetylene) and propadiene (allene), and the obtained propylene may be further processed to polypropylene.
Another important selective hydrogenation in industry is the removal of traces of 1,3-butadiene from the C4 fraction after the extractive separation thereof. Pd/Al2O3 catalysts are commonly used in this reaction. Furthermore, the selective hydrogenation of 1,5-cyclooctadiene, obtained by cyclic dimerization of 1,3-butadiene, to cyclooctene on Pd/Al2O3 and of benzene to cyclohexene on ruthenium catalysts are of importance.
For enhancing the selectivity of catalysts in selective hydrogenations, intermetallic compounds have recently attracted attention. For instance, WO 2007/104569 (claiming the priority of EP 1 834 939 A1), according to a general aspect, relates to selective hydrogenation processes using, as hydrogenation catalysts, specific ordered intermetallic compounds, which satisfy the so-called site isolation principle for the hydrogenation-active metals in the ordered intermetallic compound. The focus of the above WO publication is on ordered intermetallic compounds comprising palladium and/or platinum as hydrogenation-active metals. Concretely, PdGa, Pd3Ga7, Pd2Ga, Pd2Ge, PdZn and PtZn are tested in the selective hydrogenation of acetylene to ethylene, and the activity and selectivity of these catalysts is compared with conventional Pd/Al2O3 and Pd20Ag80 alloy catalysts. The scientific papers by J. Osswald et al. in Journal of Catalysis 258 (2008), pp. 210-218 and pp. 219-227 provide a similar teaching, while being limited to studies of the intermetallic compounds PdGa and Pd3Ga7.
High costs are connected with the use of both, palladium and platinum, so that industry has been interested in finding alternative hydrogenation catalysts that are inexpensive and nevertheless are highly active and selective, long-term stable catalysts.
The use of ordered intermetallic compounds as catalysts in a variety of different reactions is generally described in US 2004/0126267 A1 and WO 2004/012290 A2. However, these documents fail to disclose the application of this type of compounds to hydrogenations, let alone selective hydrogenations. In fact, the focus of these references is on their use in fuel cells. Moreover, they seemingly fail to mention ordered cobalt-aluminum or iron-aluminum intermetallic compounds.
U.S. Pat. No. 4,507,401 relates to supported intermetallic catalysts that are produced by a process which begins with the preparation of a supported Group VIII metal composition where the Group VIII metal includes iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum or combinations of these metals. Then, the Group VIII containing support is contacted with a metal hydride or organometallic compound at a temperature sufficient to form an intermetallic compound wherein the metal hydride or organometallic compound contains at least one metal atom selected from the group consisting of silicon, germanium, aluminum, boron, gallium, indium and tin. In the working examples of the patent, supported nickel-silicon, nickel-germanium and nickel-aluminum intermetallic compounds are prepared. The supported catalysts are tested in the hydrogenolysis and dehydrogenation of cyclohexane.
EP 0 645 464 A2 is concerned with ultrafine particles of quasi-cristalline aluminum alloys, for instance of Al65Cu20Fe15, Al65Cu20Co15, Al70Ni15CO15, Al70Pd17Fe13 and Al75Pd15CO10. The aluminum alloys are tested in methanol decomposition to yield hydrogen.
In P. A. Thiel, Annu. Rev. Phys. Chem. 2008, 59, pp. 129-52, d-Al—Ni—Co is assumed to have a good potential for service in the steam reforming of methanol.
H. Imamura et al. in The Journal of Physical Chemistry, Vol. 83, No. 15, 1979, pp. 2009-2012 describe the catalytic testing of CoAl, CO2Al9, FeAl and Fe3Al in methanation reactions.
L. V. Galaktionova et al. in Russian Journal of Physical Chemistry A, 2008, Vol. 82, No. 2, pp. 206-210 reports the conversion of CO2 and CH4 to CO and hydrogen using Fe-containing intermetallic compounds, e.g. Fe3Al and Fe2Al5.
In view of the above, it is an object of the present invention to provide a process for the hydrogenation of unsaturated hydrocarbon compounds, in particular of ethyne (acetylene) in admixture with a large excess of ethene (ethylene) to afford ethene, which overcomes the drawbacks in terms of activity and/or selectivity of the conventional hydrogenation catalysts as outlined above, and which furthermore is an inexpensive process in terms of costs of catalysts. It is another object to provide novel catalysts having the above beneficial properties in selective hydrogenation reactions, in particular in the selective hydrogenation of acetylene to afford ethylene when ethylene is present in an excessive amount.